Circuit card with flexible connection for memory module with heat spreader

ABSTRACT

A circuit card includes a rigid portion having a first plurality of contacts configured to be in electrical communication with a plurality of memory devices. The circuit card further includes a flexible connector coupled to the rigid portion. The flexible connector has a first side and a second side. The flexible connector comprises a dielectric layer, a second plurality of contacts configured to be in electrical communication with a substrate, and a plurality of electrical conduits on the first side of the flexible connector and extending from the rigid portion to the second plurality of contacts. The plurality of electrical conduits is in electrical communication with one or more contacts of the first plurality of contacts and with the second plurality of contacts. The flexible connector further includes an electrically conductive layer on the second side of the flexible connector. The electrically conductive layer is superposed with the plurality of electrical conduits with the dielectric layer therebetween. The electrically conductive layer does not cover one or more portions of the second side of the flexible connector, thereby providing improved flexibility of the flexible connector.

RELATED APPLICATIONS

This application claims the benefit of priority from U.S. ProvisionalPatent No. 60/712,156, filed Aug. 29, 2005, which is incorporated in itsentirety by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This application relates generally to electronic circuitry and modulesfor computer-based applications, and more particularly to circuit cards,printed circuit boards, and memory modules.

2. Description of the Related Art

Computer systems often utilize modules comprising one or more circuitcards or printed circuit boards (PCBs). Each PCB has one or morecomponents (e.g., integrated circuits or ICs) mounted thereon, and thecomponents can be mounted on one side or on both sides of the PCB. Incertain computer systems, the PCBs of the module are stacked next to oneanother to increase the functionality of the module. For example, boardstacking is a method used to increase the memory density in memorysubsystems. The technique is also used to increase the device density ofother components, such as logic. Stacking enhances the capability of thesubsystem, particularly if components are assembled on each of the twosides of each of the stacked PCB. In such configurations, the componentsmounted on one side of one PCB are positioned in close proximity to thecomponents mounted on a neighboring side of a neighboring PCB. Suchcomponents mounted in close proximity to the PCB can require complicatedconnections to the PCB. Stacked PCB configurations in the prior art haveused flexible circuitry or flex circuits to provide electricalconnections between the stacked PCBs, but these configurations have beenlimited by the characteristics of the flexible circuitry.

Stacking configurations can cause problems due to power dissipation inthe components which are in close proximity. Some or all of thecomponents can generate significant amounts of heat, which can raise thetemperature of the component itself or of the surrounding components ofthe module. The narrow air gap between the components on either side ofthe stacked PCBs prevents air flow which would otherwise keep thecomponents within their specified operating temperature ranges. Theraised temperature of these components can have harmful effects on theperformance of the components, causing them to malfunction.

Prior art systems utilize heat spreaders to radiate the heat away fromthe heat-generating component and away from the surrounding componentsof the module. Such prior art heat spreaders are mounted over theheat-generating component. In stacked configurations, the prior art heatspreaders are typically mounted over components on an outside surface ofthe PCB (i.e., a surface away from a neighboring PCB). While these priorart heat spreaders can dissipate heat generated by the components on theoutside surface of the PCB, components on the inside surfaces wouldremain hot. In addition, the components on the outside surface of thePCB are effectively cooled by air flowing across the component from aventilation fan. However, the narrow air gap between the stacked PCBswould allow very little cool air from the ventilation fan to cool thecomponents on the inside surfaces to within the specified operatingtemperatures.

Computer systems typically have a plurality of sockets into which memorymodules can be releasably inserted to electrically couple the memorymodule with various other components of the computer system.Conventional dual in-line memory modules (DIMMs) have a printed circuitboard (PCB) with one edge having electrical contacts which are designedto fit into these sockets and to be electrically coupled withcorresponding electrical contacts in the socket. Because these socketsare often in proximity to one another (e.g., spaced with approximately 9millimeters on either side of the socket), there is a limited amount ofspace between the sockets which thereby limits the dimensions of amemory module installed therein.

SUMMARY OF THE INVENTION

In certain embodiments, a circuit card comprises a rigid portion havinga first plurality of contacts configured to be in electricalcommunication with a plurality of memory devices. The circuit cardfurther comprises a flexible connector coupled to the rigid portion. Theflexible connector has a first side and a second side. The flexibleconnector comprises a dielectric layer, a second plurality of contactsconfigured to be in electrical communication with a substrate, and aplurality of electrical conduits on the first side of the flexibleconnector and extending from the rigid portion to the second pluralityof contacts. The plurality of electrical conduits is in electricalcommunication with one or more contacts of the first plurality ofcontacts and with the second plurality of contacts. The flexibleconnector further comprises an electrically conductive layer on thesecond side of the flexible connector. The electrically conductive layeris superposed with the plurality of electrical conduits with thedielectric layer therebetween. The electrically conductive layer doesnot cover one or more portions of the second side of the flexibleconnector, thereby providing improved flexibility of the flexibleconnector.

In certain embodiments, a memory module comprises a main printed-circuitboard (PCB) having a first side and a second side. The main PCBcomprises a plurality of edge connectors configured to be in electricalcommunication with corresponding socket connectors of a computer system.The main PCB further comprises a first plurality of contacts inelectrical communication with the plurality of edge connectors. Thememory module further comprises a first daughter circuit card positionedon the first side of the main PCB and oriented generally parallel to themain PCB. The first daughter circuit card comprises a rigid portion anda plurality of memory devices mounted thereto. The first daughtercircuit card further comprises a flexible connector and a secondplurality of contacts thereon. The second plurality of contacts is inelectrical communication with the first plurality of contacts. Theflexible connector has a first side and a second side. The flexibleconnector comprises a dielectric layer and a plurality of electricalconduits on the first side of the flexible connector. The plurality ofelectrical conduits is in electrical communication with the plurality ofmemory devices and the second plurality of contacts. The flexibleconnector further comprises an electrically conductive layer on thesecond side of the flexible connector. The electrically conductive layeris superposed with the plurality of electrical conduits with thedielectric layer therebetween. The electrically conductive layer doesnot cover one or more portions of the second side of the flexibleconnector, thereby providing improved flexibility of the flexibleconnector.

In certain embodiments, a computer system comprises a memory modulecomprising a printed-circuit board (PCB) having a first side and asecond side. The PCB comprises a plurality of edge connectors configuredto be in electrical communication with corresponding socket connectorsof a computer system. The PCB further comprises a first plurality ofcontacts in electrical communication with the plurality of edgeconnectors. The memory module further comprises a first daughter circuitcard positioned on the first side of the PCB and oriented generallyparallel to the PCB. The first daughter circuit card comprises a rigidportion and a plurality of memory devices mounted thereto. The firstdaughter circuit card further comprises a flexible connector and asecond plurality of contacts thereon. The second plurality of contactsis in electrical communication with the first plurality of contacts. Theflexible connector has a first side and a second side. The flexibleconnector comprises a dielectric layer and a plurality of electricalconduits on the first side of the flexible connector. The plurality ofelectrical conduits is in electrical communication with the plurality ofmemory devices and the second plurality of contacts. The flexibleconnector further comprises an electrically conductive layer on thesecond side of the flexible connector. The electrically conductive layeris superposed with the plurality of electrical conduits with thedielectric layer therebetween. The electrically conductive layer doesnot cover one or more portions of the second side of the flexibleconnector, thereby providing improved flexibility of the flexibleconnector.

In certain embodiments, an electronic circuit module for a computersystem comprises a first printed-circuit board (PCB) having an edgeconnector, a first side, and a second side. The electronic circuitmodule further comprises a first plurality of electrical componentsmounted on the first side of the first PCB. The first plurality ofelectrical components is electrically coupled to the edge connector. Theelectronic circuit module further comprises a second plurality ofelectrical components mounted on the second side of the second PCB. Thesecond plurality of electrical components is electrically coupled to theedge connector. The electronic circuit module further comprises a secondPCB having a first side facing towards the first PCB and a second sidefacing away from the first PCB. The electronic circuit module furthercomprises a third plurality of electrical components mounted on thefirst side of the second PCB. The electronic circuit module furthercomprises a fourth plurality of electrical components mounted on thesecond side of the second PCB. The electronic circuit module furthercomprises at least one electrical conduit between the first PCB and thesecond PCB. The at least one electrical conduit electrically couples thethird plurality of electrical components to the edge connector andelectrically couples the fourth plurality of electrical components tothe edge connector. The electronic circuit module further comprises aheat spreader comprising a thermally conductive material. The heatspreader comprises a first portion thermally coupled to the firstplurality of electrical components. The heat spreader further comprisesa second portion thermally coupled to the second plurality of electricalcomponents and to the third plurality of electrical components. The heatspreader further comprises a third portion thermally coupled to thefourth plurality of electrical components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C schematically illustrate three views of an example circuitcard having a rigid portion that includes a portion of the layers whichcomprise the flexible connector in accordance with certain embodimentsdescribed herein.

FIG. 2 schematically illustrates a side view of an example circuit cardhaving a rigid portion that includes a portion of the layers whichcomprise the flexible connector on one side of the rigid portion inaccordance with certain embodiments described herein.

FIG. 3 schematically illustrates an example circuit card having anelectrically conductive layer which comprises a plurality of metaltraces that are superposed and generally parallel with the plurality ofelectrical conduits with the dielectric layer therebetween.

FIG. 4 schematically illustrates an example circuit card having aplurality of memory devices and a plurality of passive componentsmounted thereto.

FIGS. 5A-5C schematically illustrates an example substrate that isconfigured to be electrically coupled to a circuit card compatible withcertain embodiments described herein.

FIGS. 6A-6C schematically illustrate an example circuit card configuredto be mounted to the substrate schematically illustrated by FIGS. 5A-5C.

FIG. 7A schematically illustrates an edge view of two example circuitcards compatible with FIGS. 6A-6C mounted on the substrate of FIGS.5A-5C.

FIG. 7B schematically illustrates an edge view of two example circuitcards compatible with FIG. 2 mounted on the substrate of FIGS. 5A-5C.

FIGS. 8A-8C provides an example configuration of the contacts on thefirst side and the second side of the substrate (corresponding to thecontacts on each circuit card) and the edge connector contacts of thesubstrate for a DDR1 RDIMM compatible with certain embodiments describedherein.

FIGS. 9A-9C provides an example configuration of the contacts on thefirst side and the second side of the substrate and the edge connectorcontacts of the substrate for a DDR2 RDIMM with registers and PLLcircuit elements on the circuit card compatible with certain embodimentsdescribed herein.

FIGS. 10A-10C provides an example configuration of the contacts on thefirst side and the second side of the substrate and the edge connectorcontacts of the substrate for a DDR2 RDIMM with registers and PLLcircuit elements on the substrate compatible with certain embodimentsdescribed herein

FIGS. 11A-11C schematically illustrates three views of another examplecircuit card compatible with certain embodiments described herein withsome example dimensions (in millimeters).

FIGS. 12A-12C schematically illustrate three views of the circuit cardand the substrate of FIGS. 11A-11C populated by a plurality of memorydevices and an advanced memory buffer (AMB) mounted on the circuit cardand on the substrate. FIG. 12A has the following example dimensions:α13.2 millimeters; β=8.08 millimeters; ψ=7.25 millimeters; μ=14.70millimeters; and τ=3.62 millimeters. FIG. 12C has the following exampledimensions: α=20.00 millimeters; β=7.500 millimeters; ψ=7.25millimeters; μ=18.300 millimeters; and τ=2.870 millimeters.

FIGS. 13A-13D schematically illustrate four views of an example memorymodule comprising the circuit card and the substrate in accordance withcertain embodiments described herein. FIG. 13A has the following exampledimensions: α=126.30 millimeters; β=133.33 millimeters; ψ=19.50millimeters; μ=4.04 millimeters; and τ=18.32 millimeters.

FIG. 14A schematically illustrates an edge view of the memory module ofFIGS. 13A-13D mounted in a computer system socket. FIG. 14A has thefollowing example dimensions: α=1.270 millimeters; β=7.500 millimeters;ψ=18.781 millimeters; μ=2.865 millimeters; τ=18.000 millimeters; ∈=9.500millimeters; ω=19.718 millimeters; π=1.143 millimeters; and γ=21.509millimeters.

FIG. 14B schematically illustrates an edge view of the memory module ofFIGS. 13A-13D with a heat spreader mounted thereon. FIG. 14B has thefollowing example dimensions: α=21.50 millimeters; and β=12.00millimeters.

FIG. 15 schematically illustrates a pair of example modules each havinga mother PCB and a single daughter PCB in accordance with certainembodiments described herein. FIG. 15 has the following exampledimensions: α=4 millimeters; β=9.4 millimeters; ψ=18.3 millimeters:μ=2.87 millimeters; τ=20 millimeters: and φ=5.8 millimeters.

FIG. 16 schematically illustrates another pair of example modules eachhaving a mother PCB and two daughter PCBs in accordance with certainembodiments described herein. FIG. 16 has the following exampledimensions: α=8 millimeters; β=13.5 millimeters; ψ=18.3 millimeters;μ=2.87 millimeters: and φ=2 millimeters.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1A-1C schematically illustrate three views of an example circuitcard 10 compatible with certain embodiments described herein. Thecircuit card 10 comprises a rigid portion 20 having a first plurality ofcontacts 22 configured to be in electrical communication with aplurality of memory devices (not shown). The circuit card 10 furthercomprises a flexible connector 30 coupled to the rigid portion 20. Theflexible connector 30 has a first side 32 and a second side 34. Theflexible connector 30 comprises a dielectric layer 40 and a secondplurality of contacts 50 configured to be in electrical communicationwith a substrate (not shown). The flexible connector 30 furthercomprises a plurality of electrical conduits 60 on the first side 32 ofthe flexible connector 30 and extending from the rigid portion 20 to thesecond plurality of contacts 50. The plurality of electrical conduits 60are in electrical communication with one or more contacts 22 of thefirst plurality of contacts 22 and with the second plurality of contacts50. The flexible connector 30 further comprises an electricallyconductive layer 70 on the second side 34 of the flexible connector 30.The electrically conductive layer 70 is superposed with the plurality ofelectrical conduits 60 with the dielectric layer 40 therebetween. Theelectrically conductive layer 70 does not cover one or more portions 80of the second side 34 of the flexible connector 30, thereby providingimproved flexibility of the flexible connector 30.

In certain embodiments, the rigid portion 20 is configured to have aplurality of circuit components (e.g., memory devices) mounted thereon.In certain embodiments, the rigid portion 20 is flexible prior to havingthe components mounted thereon, but is rigid once the components aremounted thereon. In certain other embodiments, the rigid portion 20 isrigid both prior to and after having the components mounted thereon. Therigid portion 20 of certain embodiments is sufficiently rigid to providestructural stability to the plurality of circuit components when thecomponents are mounted on the rigid portion 20.

The rigid portion 20 of certain embodiments comprises a printed-circuitboard (PCB) comprising a laminate structure (e.g., FR4) of fiberglasssaturated with epoxy resin and electrically conductive (e.g., copper)traces and vias. These traces and vias provide electrical conductivityto the first plurality of contacts 22. In certain embodiments, the rigidportion 20 comprises an eight-layer PCB, while in certain otherembodiments, the rigid portion 20 comprises four, six, or other numberof layers. In certain embodiments, the rigid portion 20 has a generallyrectangular shape, while in certain other embodiments, the rigid portion20 has other shapes (e.g., trapezoidal, parallelogram).

In certain embodiments, the rigid portion 20 comprises a portion of thelayers which comprise the flexible connector 30. As schematicallyillustrated by FIG. 1C, the rigid portion 20 of certain such embodimentscomprises a pair of PCBs 26 with a portion of the dielectric layer 40, aportion of the plurality of electrical conduits 60, and a portion of theelectrically conductive layer 70 sandwiched therebetween. In certainother embodiments, the rigid portion 20 has a portion of the layerswhich comprise the flexible connector 30 on one side of the rigidportion 20, as schematically illustrated by FIG. 2.

The rigid portion 20 of certain embodiments further comprises passiveelectrical components (e.g., resistors, capacitors) which are mounted onthe rigid portion 20 and are electrically coupled to the first pluralityof contacts 22. In certain such embodiments, at least some of thesepassive electrical components are mounted on at least one of the sidesof the rigid portion 20, while in certain other such embodiments, atleast some of these passive electrical components are within the rigidportion 20 (e.g., embedded between laminate layers).

In certain embodiments, as schematically illustrated by FIGS. 1A and 1B,the first plurality of contacts 22 are on both sides of the rigidportion 20. In certain other embodiments, the first plurality ofcontacts 22 is on a single side of the rigid portion 20. The firstplurality of contacts 22 of certain embodiments comprise ball-gridarrays (BGAs), while other types of contacts 22 are also compatible withcertain embodiments described herein. In certain embodiments, one ormore of the contacts 22 are electrically coupled to one or more of theelectrical conduits 60 of the flexible connector 30. In certain otherembodiments, one or more of the contacts 22 are electrically coupled tothe electrically conductive layer 70 of the flexible connector 30.

In certain embodiments, at least some of the contacts 22 are configuredto be electrically coupled to a plurality of memory devices. In certainother embodiments, at least some of the contacts 22 are configured to beelectrically coupled to other circuit components, including but notlimited to, passive electrical components (e.g., resistors, capacitors),phase-lock loop circuitry, registers, and advanced memory buffers(AMBs).

In certain embodiments, the flexible connector 30 has a laminatestructure with the dielectric layer 40 sandwiched between twoelectrically conductive layers (e.g., the plurality of electricalconduits 60 and the electrically conductive layer 70). As used herein,the term “layer” is used in its broadest ordinary meaning. For example,a layer may comprise a single material having a generally uniformthickness or may comprise multiple sublayers each comprising a differentmaterial. Although many of the layers are depicted herein as having arelatively thin sheet-like expanse or region lying over or underanother, a layer as used herein may comprise a shorter expanse or regionor multiple expanses or regions.

In certain embodiments, the flexible connector 30 has a generallyrectangular shape, while in certain other embodiments, the flexibleconnector 30 has other shapes (e.g., trapezoidal, parallelogram). Theflexible connector 30 of certain embodiments is coupled to the rigidportion 20 along at least one edge 31 of the flexible connector 30.

As schematically illustrated by FIGS. 1A-1C, the flexible connector 30of certain embodiments comprises only the dielectric layer 40, theelectrical conduits 60, and the electrically conductive layer 70. Thisconfiguration is sometimes described as “two-layer flex,” referring tothe two electrically conductive layers. In certain other embodiments,the flexible connector 30 includes four, five, or other number of layerswhich include one or more electrically conductive layers and one or moreelectrically insulating layers. For example, the flexible connector 30can comprise five layers: the three layers of FIGS. 1A-1C plus twoadditional insulating layers on either side of the conductive layers toprotect and/or insulate the conductive layers. However, generally fewerlayers are more advantageous by providing more flexibility of theflexible connector 30 as compared to structures with more layers.

In certain embodiments, the dielectric layer 40 comprises one or morepolymer materials, examples of which include, but are not limited to,polyimide (e.g., Kapton®) and polyester. The thickness of the dielectriclayer 40 of certain embodiments is in a range between about 25 micronsand about 100 microns, although other thicknesses are also compatiblewith certain embodiments described herein. In certain embodiments, thedielectric layer 40 is a generally continuous sheet of material, whilein certain other embodiments, the dielectric layer 40 has holes, slits,or other discontinuities therein. In certain embodiments, the dielectriclayer 40 has a generally rectangular shape, while in certain otherembodiments, the dielectric layer 40 has other shapes (e.g.,trapezoidal, parallelogram).

In certain embodiments, the second plurality of contacts 50 comprise anelectrically conductive material (e.g., copper) that is configured to beelectrically coupled (e.g., soldered) to corresponding contacts on asubstrate (not shown). As schematically illustrated in FIGS. 1A and 1B,the contacts 50 of certain embodiments comprise an electricallyconductive first region 52 on the first side 32 of the flexibleconnector 30, an electrically conductive second region 54 on the secondside 34 of the flexible connector 30, and a hole 56 through the flexibleconnector 30 having an inner surface coated with the electricallyconductive material and electrically coupling the first region 52 andthe second region 54. The second region 54 is generally surrounded by agap 58 in the electrically conductive layer 70 that electricallyisolates the second region 54 from the electrically conductive layer 70on the second side 34 of the flexible connector 30. While FIGS. 1A and1B schematically illustrate the first region 52 as being generallysquare and the second region 54 as being generally circular, othershapes of the first region 52 and the second region 54 are alsocompatible with certain embodiments described herein.

In certain embodiments, each of the contacts 50 of the second pluralityof contacts 50 has a diameter in a range between about 0.25 millimeterand about 0.5 millimeter. The second plurality of contacts 50 of certainembodiments are positioned generally along one edge of the flexibleconnector 30 and are spaced from one another, as schematicallyillustrated by FIGS. 1A and 1B. The pitch spacing between the contacts50 of certain embodiments is about 1 millimeter, about 0.8 millimeter,about 0.5 millimeter, or smaller.

In certain embodiments, the plurality of electrical conduits 60comprises an electrically conductive material (e.g., copper) thatelectrically couples at least some of the first plurality of contacts 22to at least some of the second plurality of contacts 50. The conduits 60of certain embodiments have a thickness in a range between about 0.025millimeter and about 0.25 millimeter. The conduits 60 of certainembodiments are spaced from one another along the first side 32 of theflexible connector 30, thereby exposing portions of the underlyingdielectric layer 40. In certain such embodiments, the conduits 60 arespaced from one another with a pitch spacing generally equal to thepitch spacing between the contacts 50. In certain embodiments, theconduits 60 extend across a length of the first side 32 of the flexibleconnector 30 and are generally straight and parallel to one another, asschematically illustrated by FIG. 1B. In certain other embodiments, atleast one conduit 60 has at least one curve or non-zero angle as itextends across the first side 32 of the flexible connector 30. Incertain embodiments, at least one conduit 60 has one or more branchpoints at which the conduit 60 branches or forks in two or more separatedirections.

As schematically illustrated by FIG. 1A, in certain embodiments, eachconduit 60 comprises a tapered section 62 connected to one of thecontacts 50 and an elongate section 64 extending along a length of thefirst side 32 of the flexible connector 30 from the rigid portion 20 tothe tapered section 62. In certain embodiments, the tapered section 62has a length in a range between about 0.8 millimeter and about 1.5millimeters and a width in a range between about 0.025 millimeter andabout 0.8 millimeter. As schematically illustrated by FIG. 1A, incertain embodiments, the portion of the tapered section 62 coupled tothe contact 50 has a width generally equal to the width of the contact50, and the portion of the tapered section 62 coupled to the elongatesection 64 has a width generally equal to the width of the elongatesection 64. The elongate section 64 of certain embodiments has a widththat is smaller than the width of the contacts 50 (e.g., in a rangebetween about 0.025 millimeter and about 0.25 millimeter).

In certain embodiments, the electrically conductive layer 70 comprisesan electrically conductive material (e.g., copper). The layer 70 ofcertain embodiments has a thickness in a range between about 17.5microns and about 70 microns. In certain embodiments, the layer 70extends generally across at least a portion of the second side 34 of theflexible connector 30. As schematically illustrated in FIG. 1B, thelayer 70 extends from a first region 72 proximate to the rigid portion20, across a second region 74, to a third region 76 superposed with thecontacts 50 on the first side 32 of the flexible connector 30, therebyproviding electrical conductivity from the first region 72 through thesecond region 74 to the third region 76.

The layer 70 of certain embodiments does not cover one or more portions80 of the second side 34 of the flexible connector 30. As schematicallyillustrated in FIG. 1B, in certain embodiments, the portions 80 of thesecond side 34 that are not covered by the layer 70 are in the secondregion 74, thereby exposing the underlying dielectric layer 40. Incertain other embodiments, the portions 80 can also be in the firstregion 72 and/or in the third region 76. Certain embodiments describedherein advantageously provide improved flexibility of the flexibleconnector 30 for bending in a direction generally perpendicular to theflexible connector 30 by having the layer 70 not cover one or moreportions 80 of the second side 34 of the flexible connector 30, therebyavoiding having conductive material over these portions 80 which wouldotherwise reduce the flexibility of the flexible connector 30.

As schematically illustrated by FIG. 1B, in certain embodiments, thelayer 70 in the second region 74 comprises a plurality of metal lines 78in a cross-hatched pattern which define the portions 80 therebetween.The portions 80 can have various shapes, including but not limited to,square, parallelogram, trapezoidal, triangular, hexagonal, circular, orcombinations thereof. For example, as schematically illustrated in FIG.1B, some of the portions 80 have a generally square shape and some ofthe portions 80 have a generally triangular shape. In certainembodiments, the metal lines 78 have a width in a range between about0.025 millimeter and about 0.25 millimeter, and a pitch spacing in arange between about 0.15 millimeter and about 1.5 millimeters. Incertain embodiments, the width of the metal lines 78 are substantiallyconstant across the length of the metal lines 78, while in certain otherembodiments, the width varies across the length of the metal lines 78.The metal lines 78 shown in FIG. 1B are generally oriented at a non-zeroangle (e.g., 45 degrees) relative to one or more edges of the flexibleconnector 30, while other orientations (e.g., parallel to at least oneedge of the flexible connector 30) are also compatible with certainembodiments described herein.

In certain other embodiments, as schematically illustrated by FIG. 3,the layer 70 in the second region 74 comprises a plurality of metaltraces 79 that are superposed and generally parallel with the pluralityof electrical conduits 60 with the dielectric layer 40 therebetween. Themetal traces 79 of certain embodiments are wider than the correspondingconduits 60 on the first side 32 of the flexible connector 30. Incertain embodiments, the width of the metal traces 79 is in a rangebetween about 0.075 millimeter and about 0.75 millimeter. In certainembodiments, the width of the metal traces 79 is substantially constantacross the length of the metal traces 79, while in certain otherembodiments, the width varies across the length of the metal traces 79.

In certain embodiments, the layer 70 serves as a ground plane for atleast a portion of the circuit card 10 along the flexible connector 30.In certain other embodiments, the layer 70 serves as a power plane forat least a portion of the circuit card 10 along the flexible connector30. By serving as a ground or power plane that is superposed with theconduits 60 on the first side 32 of the flexible connector 30, the layer70 of certain embodiments advantageously enhances signal integrity andimpedance matching of signals propagating through the conduits 60.

FIG. 4 schematically illustrates an edge view of an example circuit card10 having a plurality of memory devices 90 and a plurality of passivecomponents 100 mounted thereto. Examples of memory devices compatiblewith certain embodiments described herein include, but are not limitedto, DDR1, DDR2, or DDR3 dynamic random-access memory (DRAM) componentsin dual-die packages (DDP) with BGA connections, and with example memorycapacities such as 1 Gb (256M×4-bit) or 512 Mb (128M×4-bit). Other typesof memory devices are also compatible with certain embodiments describedherein. The memory devices 90 of certain embodiments are mounted on therigid portion 20 by a plurality of solder balls 92 as schematicallyillustrated by FIG. 4 which also provides electrical connections betweenthe contacts 22 of the rigid portion 20 and corresponding contacts ofthe memory devices 90.

FIGS. 5A-5C schematically illustrates a substrate 110 that is configuredto be electrically coupled to a circuit card 10 compatible with certainembodiments described herein. In certain embodiments, the substrate 110is a printed-circuit board with dimensions which are selected to becompatible with installation of the substrate 110 in a computer system.For example, in certain embodiments, the substrate 110 has a height of18.3 millimeters and a length of 133.0 millimeters.

In certain embodiments, the substrate 110 comprises a plurality of edgeconnector contacts 112, a first side 114, a second side 116, one or moreelectrical components 118, and a plurality of surface contacts 120. Theedge connector contacts 112 of certain embodiments are positioned alongan edge 113 of the substrate 110 on the first side 114 and on the secondside 116, and are configured to be releasably mounted to correspondingelectrical contacts of a computer system socket (not shown).

In certain embodiments, the one or more electrical components 118 aremounted on the first side 114, on the second side 116, or on both thefirst side 114 and the second side 116 of the substrate 110. Theelectrical components 118 mounted on the substrate 110 can comprisevarious circuit components, including but not limited to, passiveelectrical components (e.g., resistors, capacitors), memory devices,phase-lock loop circuitry, registers, and advanced memory buffers(AMBs).

The surface contacts 120 of certain embodiments are configured to beelectrically coupled (e.g., soldered) to the second plurality ofcontacts 50 of the circuit card 10. In certain embodiments in which thesubstrate 110 is configured to be coupled to a single circuit card 10,the surface contacts 120 are on either the first side 114 or the secondside 116 of the substrate 110. In certain other embodiments in which thesubstrate 110 is configured to be coupled to two circuit cards 10, thesurface contacts 120 are on both the first side 114 and the second side116 of the substrate 110. As schematically illustrated by FIGS. 5A and5B, the surface contacts 120 of certain embodiments are positionedgenerally along a line parallel to the edge 113 across the first side114 and generally along a line parallel to the edge 113 across thesecond side 116. In certain embodiments, the substrate 110 comprisesbetween about 100 and about 170 surface contacts 120 along one side.

In certain embodiments, the substrate 110 comprises at least onethermally conductive layer 130 that is thermally coupled to one or moreof the edge connector contacts 112 of the substrate 110. The thermallyconductive layer 130 of certain embodiments comprises copper or aluminumand is on either the first side 114, on the second side 116, or one boththe first side 114 and the second side 116 of the substrate 110. Incertain embodiments, the thermally conductive layer 130 has a thicknessin a range between about 17.5 microns and about 100 microns, a height ina range between about 8 millimeters and about 24 millimeters, and alength along the substrate 110 in a range between about 40 millimetersand about 125 millimeters. The thermally conductive layer 130 of certainembodiments is configured to provide a thermal conduit to draw heat fromthe memory devices 90 in thermal communication therewith, toadvantageously provide cooling of the memory devices 90.

FIGS. 6A-6C schematically illustrate an example circuit card 10configured to be mounted to the substrate 110 schematically illustratedby FIGS. 5A-5C. The circuit card 10 comprises a plurality of memorydevices 90 and passive electrical components 132 (e.g., resistors,capacitors) mounted thereon. As schematically illustrated by FIGS. 6Aand 6B, each circuit card 10 has 18 dynamic random-access memory (DRAM)devices 90 mounted thereon, with 10 memory devices 90 mounted on a firstside 134 of the rigid portion 20 and 8 memory devices 90 mounted on asecond side 136 of the rigid portion 20. The memory devices 90 on thesecond side 136 of the circuit card 10 are configured to leave a portion138 of the second side 136 generally free from electrical componentsmounted thereon.

FIG. 7A schematically illustrates an edge view of an example memorymodule 200 comprising two circuit cards 10 compatible with FIGS. 6A-6Cmounted on the substrate 110 of FIGS. 5A-5C. FIG. 7B schematicallyillustrates an edge view of an example memory module 200 comprising twocircuit cards 10 compatible with FIG. 2 mounted on the substrate 110 ofFIGS. 5A-5C. Exemplary memory modules compatible with certainembodiments described herein include, but are not limited to, dualin-line memory modules (DIMMs) such as fully-buffered DIMMs (FBDIMMs).In certain embodiments, the memory module 200 of FIG. 7A is a 4 GBmemory module with thirty-six memory devices (e.g., DDR2 256M×4-bit, 1Gb DDP DRAM components) arranged in four ranks. In certain embodiments,the memory module 200 of FIG. 7B is a 4 GB memory module with eighteen 2Gb DDP memory devices arranged in two ranks. Example ranks compatiblewith certain embodiments described herein are blocks of memory of afixed depth and having either an “×64-bit” or an “×72-bit” width. Forexample, 16 or 18 “×4” memory components can be used to form a rank ofmemory, while 8 or 9 “×8” memory components can be used to form a rankof memory.

While each of FIGS. 7A and 7B schematically illustrates a memory module200 with two circuit cards 10 mounted on the substrate 110, in certainother embodiments, the memory module 200 comprises only a single circuitcard 10 mounted on the substrate 110. Each circuit card 10 is mountedsuch that the memory devices 90 on the first side 134 of the rigidportion 20 are facing away from the substrate 110 and the memory devices90 on the second side 136 of the rigid portion 20 are in thermal contactwith the thermally conductive layer 130 of the substrate 110. In certainembodiments, a thermally conductive film placed between the memorydevices 90 on the second side 136 of the rigid portion 20 and thethermally conductive layer 130 of the substrate 110 advantageouslyenhances the thermal conductivity between the memory devices 90 and thethermally conductive layer 130. The circuit card 10 mounted on the firstside 114 of the substrate 110 is positioned so that the portion 138 ofits second side 136 is in proximity to the electrical components 118 onthe first side 114 of the substrate 110. Similarly, the circuit card 10mounted on the second side 116 of the substrate 110 is positioned sothat the portion 138 of its second side 136 is in proximity to theelectrical components 118 on the second side 116 of the substrate 110.

In certain embodiments, the contacts 50 of the flexible connector 30 aresoldered to the corresponding contacts 120 of the substrate 110. Incertain other embodiments, an anisotropic conductive film (ACF) is usedto electrically couple the contacts 50 with the contacts 120. Otherembodiments can use other means (e.g., conductive epoxy) to electricallycouple the contacts 50 with the contacts 120.

As schematically illustrated by FIGS. 7A and 7B, the flexible connector30 of certain embodiments is bent by an angle greater than 90 degrees(e.g., by 180 degrees). The first side 32 of the flexible connector 30is on an outer curve of the bend, and the second side 34 of the flexibleconnector 30 is on an inner curve of the bend. As described above andshown schematically in FIG. 1A, in certain embodiments, the taperedportion 62 of each electrical conduit 60 has a width that decreases fromthe contact 50 to the elongate portion 64 of the electrical conduit 60.In certain such embodiments, the tapered portions 62 advantageouslyprevent the flexible connector 30 from bending with a radius ofcurvature smaller than a desired radius, thereby avoiding excessivestress and strain on the flexible connector 30 and on the electricalconnection between the contact 50 and the contact 120. In certain suchembodiments, the tapered portions 62 thus advantageously reduce thefailure rate of the flexible connectors 30. In certain embodiments, theflexible connector 30 is bent with a radius of curvature greater thanabout 0.8 millimeter.

The memory module 200 of certain embodiments further comprises a heatspreader 210, as schematically illustrated by FIGS. 7A and 7B. The heatspreader 210 comprises a thermally conductive material (e.g., copper,aluminum) and is in thermal contact with some or all of the memorydevices 90 on the first side 134 of the rigid portion 20. The heatspreader 210 of certain embodiments is configured to provide a thermalconduit to draw heat from the memory devices 90 in thermal communicationtherewith, to provide cooling of the memory devices 90. In certainembodiments, a thermally conductive film is placed between the memorydevices 90 on the first side 134 of the rigid portion 20 and the heatspreader 210 to advantageously enhance the thermal conductivity betweenthe memory devices 90 and the heat spreader 210. The heat spreader 210of certain embodiments comprises a plurality of sections which fittogether, while in certain other embodiments, the heat spreader 210 is asingle unitary piece of material. In certain embodiments, the overallthickness of the memory module 200 including the heat spreader 210 isabout 10.55 millimeters.

In certain embodiments, the contacts 50 of the flexible connector 30 andthe contacts 120 of the substrate 110 are advantageously configured suchthat the circuit card 10 can be mounted to either the first side 114 orthe second side 116 of the substrate 110. By having circuit cards 10that are compatible for mounting on either side of the substrate 110,certain such embodiments advantageously avoid the necessity of providingand keeping track of two types of circuit cards 10, one for mounting oneach side of the substrate 110.

FIGS. 8A-8C provides an example configuration of the contacts 120 on thefirst side 114 and the second side 116 of the substrate 110(corresponding to the contacts 50 on each circuit card 10) and the edgeconnector contacts 112 of the substrate 110 for a DDR1 registered dualin-line memory module (RDIMM) compatible with certain embodimentsdescribed herein. FIGS. 9A-9C provides an example configuration of aDDR2 RDIMM with registers and PLL circuit elements on the circuit card10 compatible with certain embodiments described herein. FIGS. 10A-10Cprovides an example configuration of the contacts 120 and the edgeconnector contacts 112 of a DDR2 RDIMM with registers and PLL circuitelements on the substrate 110 compatible with certain embodimentsdescribed herein. In each of the embodiments of FIGS. 8A-8C, 9A-9C, and10A-10C, the contacts 50 of both circuit cards 10 connected to thecontacts 120 on the first side 114 and the second side 116 of thesubstrate 110 are identical. Therefore, a circuit card 10 of certainsuch embodiments is advantageously used on either side of the substrate110.

FIGS. 11A-11C schematically illustrate three views of another examplecircuit card 10 compatible with certain embodiments described hereinwith example dimensions (in millimeters). The circuit card 10 comprisesa rigid portion 20 with a plurality of contacts 22 configured to be inelectrical communication with a plurality of electrical components(e.g., memory devices 90). The circuit card 10 further comprises aplurality of flexible connectors 30, each of which is coupled to therigid portion 20. One or more of the flexible connectors 30 has a firstside 32 and a second side 34, and comprises a dielectric layer 40, asecond plurality of contacts 50 configured to be in electricalcommunication with a substrate 110, a plurality of electrical conduits60 on the first side 32 of the flexible connector 30, and anelectrically conductive layer 70 on the second side 34 of the flexibleconnector 30.

One or more of the flexible connectors 30 are compatible with theflexible connector 30 schematically illustrated by FIGS. 1A-1C, 2, and3. The electrical conduits 60 of the flexible connector 30 extend fromthe rigid portion 20 to the second plurality of contacts 50 of theflexible connector 30. The electrical conduits 60 of the flexibleconnector 30 are in electrical communication with one or more contacts22 of the rigid portion 20 and one or more contacts 50 of the flexibleconnector 30. The electrically conductive layer 70 is superposed withthe plurality of electrical conduits 60 with the dielectric layer 40therebetween. The electrically conductive layer 70 does not cover one ormore portions 80 of the second side 34 of the flexible connector 30,thereby providing improved flexibility of the flexible connector 30.

In certain embodiments, as schematically illustrated by FIGS. 11A-11C,the flexible connector 30 is coupled to the rigid portion 20 along afirst edge 31 of the flexible connector 30 and is not coupled to therigid portion 20 along a second edge 33 of the flexible connector 30.The flexible connector 30 of certain such embodiments is free to bend ina direction generally perpendicular to the flexible connector 30.

In certain embodiments, the substrate 110 comprises a plurality of edgeconnector contacts 112, a plurality of component contacts 117, and aplurality of surface contacts 120. The edge connector contacts 112 ofcertain embodiments are configured to be releasably mounted tocorresponding contacts of a computer system socket 119. The componentcontacts 117 of certain embodiments are configured to be electricallycoupled to a plurality of electrical components 118 (e.g., memorydevices 90). The surface contacts 120 of certain embodiments areconfigured to be electrically coupled to the second plurality ofcontacts 50 of the circuit card 10.

In certain embodiments, as schematically illustrated by FIGS. 11A-11C,the circuit card 10 and the substrate 110 are coupled together by one ormore flexible circuits 220. The flexible circuit 220 of certainembodiments comprises a dielectric layer 240, a plurality of electricalconduits 260 on a first side of the flexible circuit 220, and anelectrically conductive layer 270 on a second side of the flexiblecircuit 220. In certain such embodiments, the electrically conductivelayer 270 is superposed with the plurality of electrical conduits 260with the dielectric layer 240 therebetween. The electrically conductivelayer 270 of certain embodiments does not cover one or more portions 280of the second side of the flexible circuit 220, thereby providingimproved flexibility of the flexible circuit 220. The flexible circuit220 of certain embodiments includes one or more of the various featuresdescribed above with regard to the flexible connector 30, including butnot limited to tapered portions of the conduits 260, the cross-hatchedmetal lines of the electrically conductive layer 270, and the metaltraces of the electrically conductive layer 270.

FIGS. 12A-12C schematically illustrate three views of the circuit card10 and the substrate 110 of FIGS. 11A-11C populated by a plurality ofmemory devices 90 and an advanced memory buffer (AMB) 300 mounted on thecircuit card 10 and on the substrate 110. The circuit card 10 and thesubstrate 110 schematically illustrated by FIGS. 12A-12C are configuredto be used in an FBDIMM. In addition, FIGS. 12A and 12C provide someexample dimensions (in millimeters) of the populated circuit card 10 andsubstrate 110 in accordance with certain embodiments described herein.Other dimensions are also compatible with various embodiments describedherein.

As schematically illustrated by FIGS. 12A-12C, the circuit card 10 ofcertain embodiments is populated by 16 memory devices 90 (e.g., DDR2DRAM devices and one AMB 300 mounted thereon. In certain embodiments,the AMB 300 has dimensions of about 24.5 millimeters by 19.5 millimetersby 2.4 millimeters. Example AMBs compatible with certain embodimentsdescribed herein are available from Intel Corp. of Santa Clara, Calif.,Integrated Device Technology, Inc. of San Jose, Calif., and NECElectronics America of Santa Clara, Calif. In addition, the circuit card10 can also comprise other electrical components including, but notlimited to passive electrical components (e.g., resistors, capacitors).The substrate 110 of certain embodiments is populated by 20 memorydevices 90 mounted thereon, which are substantially identical or similarto those mounted on the circuit card 10.

FIGS. 13A-13D schematically illustrate four views of a memory module 400comprising the circuit card 10 and the substrate 110 in accordance withcertain embodiments described herein. FIG. 13A schematically illustratesa view of the side of the memory module 400 having the AMB 300, and FIG.13C schematically illustrates a view of the side of the memory module400 opposite to the side of FIG. 13A. FIG. 13B schematically illustratesa top view of the memory module 400, and FIG. 13D schematicallyillustrates a bottom view. FIGS. 13A and 13B provide some exampledimensions (in millimeters) of the memory module 400, but otherdimensions are also compatible with various embodiments describedherein. The memory module 400 is formed by bending the flexible circuit220 to fold the circuit card 10 towards the substrate 110, and byelectrically coupling (e.g., soldering) the contacts 50 of the circuitcard 10 to the corresponding contacts 120 of the substrate 110.Exemplary memory modules compatible with certain embodiments describedherein include, but are not limited to, dual in-line memory modules(DIMMs) such as fully-buffered DIMMs (FBDIMMs).

FIG. 14A schematically illustrates an edge view of the memory module 400mounted in a computer system socket 119 with some example dimensions (inmillimeters). FIG. 14B schematically illustrates an edge view of thememory module 400 with a heat spreader 410 mounted thereon. The heatspreader 410 comprises a thermally conductive material (e.g., copper,aluminum) and is in thermal contact with the memory modules 90 mountedon the circuit card 10 and on the substrate 110, and is in thermalcontact with the AMB 300. In certain embodiments, a thermally conductivefilm is placed between the memory devices 90 and the heat spreader 410and between the AMB 300 and the heat spreader 410 to advantageouslyenhance the thermal conductivity between the memory devices 90 and theheat spreader 410 and between the AMB 300 and the heat spreader 410. Theheat spreader 410 of certain embodiments comprises a plurality ofsections which fit together, while in certain other embodiments, theheat spreader 410 is a single unitary piece of material.

FIG. 15 schematically illustrates a pair of example modules 500 eachhaving a single daughter PCB in accordance with certain embodimentsdescribed herein with example dimensions (in millimeters). While themodule 500 of FIG. 15 is shown in a vertical configuration, personsskilled in the art using the present disclosure are able to utilizeother orientations of the module 500. The module 500 schematicallyillustrated by FIG. 15 comprises a mother PCB 512 having an edgeconnector 514, a first side 516, and a second side 518. The module 500further comprises a first plurality of electrical components 520 mountedon the first side 516 of the mother PCB 512 and a second plurality ofelectrical components 522 mounted on the second side 518 of the motherPCB 512. The first plurality of electrical components 520 areelectrically coupled to the edge connector 514 and the second pluralityof electrical components 522 are electrically coupled to the edgeconnector 514. The module 510 further comprises at least one daughterPCB 530 having a first side 532 facing towards the mother PCB 512 and asecond side 534 facing away from the mother PCB 512. The module 500further comprises a third plurality of electrical components 540 mountedon the first side 532 of the daughter PCB 530 and a fourth plurality ofelectrical components 542 mounted on the second side 534 of the daughterPCB 530. The module 500 further comprises at least one spacer 550between the mother PCB 512 and the daughter PCB 530. The spacer 550electrically couples the third plurality of electrical components 540 tothe edge connector 514, and electrically couples the fourth plurality ofelectrical components 542 to the edge connector 514. The module 500further comprises a heat spreader 560 comprising a thermally conductivematerial (e.g., copper, aluminum). The heat spreader 560 has a firstportion 562 thermally coupled to the first plurality of electricalcomponents 520, a second portion 564 thermally coupled to the secondplurality of electrical components 522 and to the third plurality ofelectrical components 540, and a third portion 566 thermally coupled tothe fourth plurality of electrical components 542.

In certain embodiments, the module 500 is a memory module. Examplememory modules compatible with certain embodiments described hereininclude, but are not limited to, DIMMs such as fully-buffered dualin-line memory modules (FBDIMMs). In certain embodiments, the firstplurality of electrical components 520, the second plurality ofelectrical components 522, the third plurality of electrical components540, and the fourth plurality of electrical components 542 each comprisememory components. Example memory components compatible with certainembodiments described herein include, but are not limited to, DDR2dynamic random-access memory (DRAM) components in dual-die packages(DDP) with ball-grid array (BGA) connections, and with exemplary memorycapacities such as 1 Gb (256M×4-bit) or 512 Mb (128M×4-bit).

In certain embodiments, the mother PCB 512 comprises a laminate material(e.g., FR4) comprising fiberglass saturated with epoxy resin and furthercomprises electrically conductive (e.g., copper) traces and vias towhich the first plurality of electrical components 520 and the secondplurality of electrical components 522 are electrically coupled. Thesetraces and vias provide electrical conductivity between the edgeconnector 514 and the first plurality of electrical components 520 andbetween the edge connector 514 and the second plurality of electricalcomponents 522. In certain embodiments, the mother PCB 512 furthercomprises passive electrical components 570 (e.g., resistors,capacitors) which are mounted on the mother PCB 512 and are electricallycoupled to the first plurality of electrical components 520 and thesecond plurality of electrical components 522. In certain suchembodiments, at least some of these passive electrical components 570are mounted on at least one of the first side 516 and the second side518 of the mother PCB 512, while in certain other such embodiments, atleast some of these passive electrical components 570 are within themother PCB 512 (e.g., embedded between laminate layers).

In certain embodiments, the mother PCB 512 has dimensions which areselected to be compatible with installation of the module 500 in thecomputer system. For example, in certain embodiments, the mother PCB 512has a height of 18.3 millimeters.

The edge connector 514 of the mother PCB 512 is configured to bereleasably mounted to a corresponding socket 580 of the computer system,as schematically illustrated by FIGS. 15 and 16. In certain embodiments,the first plurality of electrical components 520 comprise memorycomponents which are mounted on the first side 516 of the mother PCB 512in a first row, and the second plurality of electrical components 522comprise memory components which are mounted on the second side 518 ofthe mother PCB 512 in a second row. In certain such embodiments, each ofthe first row and the second row of the mother PCB 512 comprises eightor nine memory components.

In certain embodiments, the at least one daughter PCB 530 comprises alaminate material (e.g., FR4) comprising fiberglass saturated with epoxyresin and further comprises electrically conductive (e.g., copper)traces and vias to which the third plurality of electrical components540 and the fourth plurality of electrical components 542 areelectrically coupled. These traces and vias provide electricalconductivity between the spacer 550 and the third plurality ofelectrical components 540 and between the spacer 550 and the fourthplurality of electrical components 542. In certain embodiments, thedaughter PCB 530 further comprises passive electrical components 570(e.g., resistors, capacitors) which are mounted on the daughter PCB 530.In certain such embodiments, at least some of these passive electricalcomponents 570 are mounted on at least one of the first side 532 and thesecond side 534 of the daughter PCB 530, while in certain other suchembodiments, at least some of these passive electrical components 570are within the daughter PCB 530 (e.g., embedded between laminatelayers).

In certain embodiments, the daughter PCB 530 has dimensions which areselected to be compatible with installation of the module 510 in thecomputer system. For example, in certain embodiments, the daughter PCB530 has a height of 20 millimeters. As schematically illustrated inFIGS. 15 and 16, in certain embodiments, the daughter PCB 530 extendsalong the side of the socket 580. The thickness of the socket 580 incertain such embodiments provides a limit to a minimum distance betweenthe mother PCB 512 and the daughter PCB 530, as well as a minimum totalthickness of the module 510. As can be seen in FIGS. 15 and 16, smallerthicknesses of the socket 580 correspond to smaller minimum thicknessesof the module 500. In certain embodiments, the height of the socket 580provides a limit to a maximum height of the daughter PCB 530, as well asa maximum height of the module 500. As can be seen in FIGS. 15 and 16,smaller heights of the socket 580 correspond to smaller heights of themodule 500.

In certain embodiments, the third plurality of electrical components 540comprise memory components which are mounted on the first side 532 ofthe daughter PCB 530 in a first row, and the fourth plurality ofelectrical components 542 comprise memory components which are mountedon the second side 534 of the daughter PCB 530 in a second row. Incertain such embodiments, each of the first row and the second row ofthe daughter PCB 530 comprises eight or nine memory components.

In certain embodiments, the memory components of the first and secondrows of the mother PCB 512 and the first and second rows of the daughterPCB 530 form four ranks of memory components. For example, for themodule 500 schematically illustrated by FIG. 15, 36 memory components(e.g., DDR2 256M×4-bit, 1G DDP DRAM components) can be used to form atwo-rank memory module (e.g., a two-rank FBDIMM). Example rankscompatible with embodiments described herein are blocks of memory of afixed depth and having either an “×64-bit” or an “×72-bit” width. Forexample, 16 or 18 “×4” memory components can be used to form a rank ofmemory, while 8 or 9 “×8” memory components can be used to form a rankof memory.

In certain embodiments (e.g., in which the module 500 is an FBDIMM), thefourth plurality of electrical components 542 comprises an advancedmemory buffer 590 (AMB), as schematically illustrated in FIG. 15. Incertain embodiments, the AMB 590 has dimensions of approximately 24.5millimeters by 19.5 millimeters by 2.4 millimeters. Example AMBscompatible with certain embodiments described herein are available fromIntel Corp. of Santa Clara, Calif., Integrated Device Technology, Inc.of San Jose, Calif., and NEC Electronics America of Santa Clara, Calif.In certain embodiments, as schematically illustrated by FIG. 15, thelarger height of the daughter PCB 530, as compared to the height of themother PCB 512 advantageously provides space in which to mount the AMB590. In certain embodiments, an FBDIMM can be implemented within a verylow profile (VLP) form factor.

FIG. 16 schematically illustrates another pair of example modules 500each having two daughter PCBs in accordance with certain embodimentsdescribed herein with example dimensions (in millimeters). While themodule 500 of FIG. 16 is shown in a vertical configuration, personsskilled in the art using the present disclosure are able to utilizeother orientations of the module 500. In certain embodiments (e.g., inwhich the module 500 is a four-rank DIMM), the module 500 of FIG. 16comprises a first daughter PCB 530 a and a second daughter PCB 530 b.The third plurality of electrical components 540 a comprises memorycomponents mounted on the first side 532 a of the first daughter PCB 530a facing the mother PCB 512, and the fourth plurality of electricalcomponents 542 a comprises memory components mounted on the second side534 a of the first daughter PCB 530 a. The module 500 further comprisesa fifth plurality of electrical components 540 b comprising memorycomponents mounted on the first side 532 b of the second daughter PCB530 b facing the mother PCB 512, and a sixth plurality of electricalcomponents 542 b comprising memory components mounted on the second side534 b of the second daughter PCB 542 b.

In certain embodiments, the memory components of the third plurality ofelectrical components 540 a are mounted in a row and the memorycomponents of the fourth plurality of electrical components 542 a aremounted in two rows. For example, as schematically illustrated in FIG.16, one row of memory components can be mounted on an upper portion(e.g., upper half) of the first side 532 a of the first daughter PCB 530a and another row of memory components can be mounted on a lower portion(e.g., lower half) of the second side 534 b of the first daughter PCB530 a. Similarly, in certain embodiments as schematically illustrated inFIG. 16, the memory components of the fifth plurality of electricalcomponents 540 b are mounted in a row and the memory components of thesixth plurality of memory components 542 b are mounted in two rows. Incertain such embodiments, each row of the first daughter PCB 530 a andthe second daughter PCB 530 b comprises eight or nine memory components.

In certain embodiments the memory components of the mother PCB 512 andof the two daughter PCBs 530 a, 530 b form four ranks of memorycomponents. For example, for the module 500 schematically illustrated byFIG. 16, 72 memory components (e.g., DDR400 128M×4-bit, 512 Mb DRAMcomponents) can be used to form a four-rank memory module (e.g., afour-rank DIMM with 4 GB×4 memory capacity).

In certain embodiments, as schematically illustrated by FIG. 16, thelarger height of the daughter PCBs 530 a, 530 b as compared to theheight of the mother PCB 512, advantageously provides space in which tomount additional memory components. In certain embodiments, a four-rankmemory module can be implemented within a very low profile (VLP) formfactor.

Besides providing an electrical conduit between the daughter PCB 530 andthe mother PCB 512, in certain embodiments, the spacer 550 between themother PCB 512 and the daughter PCB 530 provides mechanical stability tothe module 500 by supporting the daughter PCB 530 on the mother PCB 512.In certain such embodiments, the spacer 550 comprises one or more pinswhich are mechanically mounted to the mother PCB 512 and to the daughterPCB 530. In certain embodiments, the spacer 550 comprises a flexibleelectrical conduit between the mother PCB 512 and the daughter PCB 530.Examples of flexible electrical conduits compatible with certainembodiments described herein include, but are not limited to, flexcircuits and wire jumpers. In certain embodiments compatible with theexemplary module 500 of FIG. 16, the spacer 550 provides an electricalconduit for chip-select signals to complete a rank of memory using onerow of memory modules from the first daughter PCB 530 a and one row ofmemory modules from the second daughter PCB 530 b.

The heat spreader 560 of certain embodiments is configured to removeheat away from the electrical components of the module 500. In certainembodiments, the heat spreader 560 comprises a plurality of separablesections that are held in place on at least one of the mother PCB 512and the at least one daughter PCB 530 by a clip. In certain otherembodiments, the heat spreader 560 is held in place by beingmechanically coupled to the electrical components to which the heatspreader 560 is thermally coupled. In certain other embodiments, theheat spreader 560 is thermally coupled (e.g., by contacting or bysoldering) to one or more traces or vias of the mother PCB 512, therebyproviding a conduit for heat from the heat spreader 560, through theedge connector 514, to other portions of the computer system.

In certain embodiments, as schematically illustrated by FIG. 15, thefirst portion 562 of the heat spreader 560 covers and is thermallycoupled to the first plurality of electrical components 520. The secondportion 564 of the heat spreader 560 is sandwiched between, and isthermally coupled to, the second plurality of electrical components 522and the third plurality of electrical components 540. The third portion566 of the heat spreader 560 covers and is thermally coupled to thefourth plurality of electrical components 542. In certain embodiments,as schematically illustrated by FIG. 15, the heat spreader 560 furthercomprises a fourth portion 568 which is generally perpendicular to thefirst portion 562, the second portion 564, and the third portion 566,and which provides mechanical stability to the heat spreader 560 as wellas additional thermal capacity to diffuse heat away from the electricalcomponents.

In certain embodiments, the module 500 advantageously uses the limitedspace between sockets 580 of the computer system to provide ahigh-density memory module with capability to dissipate heat away fromthe electrical components of the module 500. For example, asschematically illustrated by FIG. 15, the spacing of the sockets 580 isapproximately 15.2 millimeters, each of the first portion 562, thesecond portion 564, and the third portion 566 of the heat spreader 560has a thickness of approximately 0.5 millimeters, the AMB 590 has athickness of approximately 2 millimeters, the daughter PCB 530 has athickness of approximately 1 millimeter, the memory modules each have athickness of approximately 1.2 millimeters, and the mother PCB 512 has athickness of approximately 1.3 millimeters. Thus, in certainembodiments, the module 500 has a total thickness of approximately 9.4millimeters and there is a gap of approximately 5.8 millimeters betweenthe two modules 500. Similarly, each of the example modules 500 of FIG.16 has a total thickness of approximately 13.5 millimeters, with a gapof approximately 2 millimeters between the two modules 500. By using athinner material for the mother PCB 512, the daughter PCB 530, or theheat spreader 560, certain embodiments can decrease the total thicknessof the module 500.

Certain embodiments of the module 500 advantageously reduce the cost ofventilation. Certain embodiments of the module 500 advantageously allowproper operation of the electrical components (e.g., ICs) of the module500 by maintaining temperatures within the desired operation range.

Certain embodiments described herein are useful in various computersystems, examples of which include but are not limited to networkservers, workstations, personal computers, mainframe computers and thelike. The computer system will typically include one or more inputdevices, such as a mouse, trackball, touchpad, and/or keyboard, adisplay, and computer-readable memory media, such as random-accessmemory (RAM) integrated circuits and a hard-disk drive. It will beappreciated that one or more portions of the computer system, includingsome or all of the software code, may be remote from the user and, forexample, resident on a network resource, such as a LAN server, Internetserver, network storage device, etc.

Various specific embodiments have been described above. Although thepresent invention has been described with reference to these specificembodiments, the descriptions are intended to be illustrative of theinvention and are not intended to be limiting. Various modifications andapplications may occur to those skilled in the art without departingfrom the true spirit and scope of the invention as defined in theappended claims.

1. A circuit card comprising: a rigid portion having a first pluralityof contacts configured to be in electrical communication with aplurality of memory devices; and a flexible connector coupled to therigid portion, the flexible connector having a first side and a secondside, the flexible connector comprising: a dielectric layer; a secondplurality of contacts configured to be in electrical communication witha substrate; a plurality of electrical conduits on the first side of theflexible connector and extending from the rigid portion to the secondplurality of contacts, the plurality of electrical conduits inelectrical communication with one or more contacts of the firstplurality of contacts and with the second plurality of contacts; and anelectrically conductive layer on the second side of the flexibleconnector, the electrically conductive layer superposed with theplurality of electrical conduits with the dielectric layer therebetween,wherein the electrically conductive layer does not cover one or moreportions of the second side of the flexible connector, thereby providingimproved flexibility of the flexible connector.
 2. The circuit card ofclaim 1, wherein the rigid portion comprises a printed-circuit board. 3.The circuit card of claim 2, wherein the printed-circuit board comprisesFR4 material.
 4. The circuit card of claim 2, wherein theprinted-circuit board is an eight-layer printed-circuit board.
 5. Thecircuit card of claim 2, wherein the rigid portion further comprises aportion of the dielectric layer, a portion of the plurality ofelectrical conduits, and a portion of the electrically conductive layer.6. The circuit card of claim 5, wherein the rigid portion comprises tworigid printed-circuit boards with the portion of the dielectric layer,the portion of the plurality of electrical conduits, and the portion ofthe electrically conductive layer sandwiched therebetween.
 7. Thecircuit card of claim 1, wherein the first plurality of contactscomprises a ball-grid array.
 8. The circuit card of claim 1, wherein thedielectric layer comprises a polymer material.
 9. The circuit card ofclaim 1, wherein the electrically conductive layer comprises a pluralityof metal lines in a cross-hatched pattern which define the portionstherebetween which are not covered by the electrically conductive layer.10. The circuit card of claim 1, wherein the electrically conductivelayer comprises a plurality of metal traces that are superposed andgenerally parallel with the plurality of electrical conduits with thedielectric layer therebetween, the metal traces defining regionstherebetween in which the electrically conductive layer does not coverthe portion of the second side of the flexible connector.
 11. Thecircuit card of claim 1, wherein the electrically conductive layer is aground plane.
 12. The circuit card of claim 1, wherein the electricallyconductive layer is a power plane.
 13. The circuit card of claim 1,wherein each contact of the second plurality of contacts comprises ahole extending from the first side of the flexible connector to thesecond side of the flexible connector.
 14. The circuit card of claim 1,wherein each electrical conduit has a tapered section connected to acorresponding one of the contacts of the second plurality of contactsand an elongate section extending along a length of the first side ofthe flexible connector from the rigid portion to the tapered section.15. A memory module comprising: a main printed-circuit board (PCB)having a first side and a second side, the main PCB comprising aplurality of edge connectors configured to be in electricalcommunication with corresponding socket connectors of a computer system,the main PCB further comprising a first plurality of contacts inelectrical communication with the plurality of edge connectors; and afirst daughter circuit card positioned on the first side of the main PCBand oriented generally parallel to the main PCB, the first daughtercircuit card comprising a rigid portion and a plurality of memorydevices mounted thereto, the first daughter circuit card furthercomprising a flexible connector and a second plurality of contactsthereon, the second plurality of contacts in electrical communicationwith the first plurality of contacts, the flexible connector having afirst side and a second side, the flexible connector comprising: adielectric layer; a plurality of electrical conduits on the first sideof the flexible connector, the plurality of electrical conduits inelectrical communication with the plurality of memory devices and thesecond plurality of contacts; and an electrically conductive layer onthe second side of the flexible connector, the electrically conductivelayer superposed with the plurality of electrical conduits with thedielectric layer therebetween, wherein the electrically conductive layerdoes not cover one or more portions of the second side of the flexibleconnector, thereby providing improved flexibility of the flexibleconnector.
 16. The memory module of claim 15, wherein the flexibleconnector is bent by an angle greater than 90 degrees.
 17. The memorymodule of claim 16, wherein the flexible connector is bent by an angleof about 180 degrees.
 18. The memory module of claim 15, wherein themain PCB comprises a first thermally conductive layer on the first sideof the main PCB, the first thermally conductive layer providing thermalcommunication between one or more memory devices of the first daughtercircuit card and one or more edge connectors.
 19. The memory module ofclaim 15, wherein the main PCB further comprises a third plurality ofcontacts in electrical communication with the plurality of edgeconnectors, the memory module further comprises a second daughtercircuit card positioned on the second side of the main PCB and orientedgenerally parallel to the main PCB, the second daughter circuit cardcomprising a rigid portion and a plurality of memory devices mountedthereto, the second daughter circuit card further comprising a flexibleconnector and a fourth plurality of contacts thereon, the fourthplurality of contacts in electrical communication with the thirdplurality of contacts, wherein the second daughter circuit card issubstantially identical to the first daughter circuit card.
 20. Thememory module of claim 19, wherein the main PCB comprises a firstthermally conductive layer on the first side of the main PCB, the firstthermally conductive layer providing thermal communication between oneor more memory devices of the first daughter circuit card and one ormore edge connectors, and wherein the main PCB comprises a secondthermally conductive layer on the second side of the main PCB, thesecond thermally conductive layer providing thermal communicationbetween one or more memory devices of the second daughter circuit cardand one or more edge connectors.
 21. The memory module of claim 15,wherein the first plurality of contacts and the second plurality ofcontacts are connected to one another by solder.
 22. The memory moduleof claim 15, wherein the main PCB comprises electronic componentsmounted thereon.
 23. The memory module of claim 15, wherein the main PCBcomprises a plurality of memory devices mounted thereon.
 24. The memorymodule of claim 23, wherein the plurality of memory devices of the mainPCB are mounted on the first side of the main PCB.
 25. The memory moduleof claim 24, further comprising a heat spreader in thermal communicationwith one or more memory devices of the main PCB and with one or morememory devices of the first daughter circuit card.
 26. The memory moduleof claim 25, wherein at least a portion of the heat spreader issandwiched between one or more memory devices of the main PCB and one ormore memory devices of the first daughter circuit card.
 27. The memorymodule of claim 15, further comprising a heat spreader in thermalcommunication with one or more memory devices of the first daughtercircuit card.
 28. A computer system comprising a memory modulecomprising: a printed-circuit board (PCB) having a first side and asecond side, the PCB comprising a plurality of edge connectorsconfigured to be in electrical communication with corresponding socketconnectors of a computer system, the PCB further comprising a firstplurality of contacts in electrical communication with the plurality ofedge connectors; and a first daughter circuit card positioned on thefirst side of the PCB and oriented generally parallel to the PCB, thefirst daughter circuit card comprising a rigid portion and a pluralityof memory devices mounted thereto, the first daughter circuit cardfurther comprising a flexible connector and a second plurality ofcontacts thereon, the second plurality of contacts in electricalcommunication with the first plurality of contacts, the flexibleconnector having a first side and a second side, the flexible connectorcomprising: a dielectric layer; a plurality of electrical conduits onthe first side of the flexible connector, the plurality of electricalconduits in electrical communication with the plurality of memorydevices and the second plurality of contacts; and an electricallyconductive layer on the second side of the flexible connector, theelectrically conductive layer superposed with the plurality ofelectrical conduits with the dielectric layer therebetween, wherein theelectrically conductive layer does not cover one or more portions of thesecond side of the flexible connector, thereby providing improvedflexibility of the flexible connector.
 29. An electronic circuit modulefor a computer system, the module comprising: a first printed-circuitboard (PCB) having an edge connector, a first side, and a second side; afirst plurality of electrical components mounted on the first side ofthe first PCB, the first plurality of electrical components electricallycoupled to the edge connector; a second plurality of electricalcomponents mounted on the second side of the second PCB, the secondplurality of electrical components electrically coupled to the edgeconnector; a second PCB having a first side facing towards the first PCBand a second side facing away from the first PCB; a third plurality ofelectrical components mounted on the first side of the second PCB; afourth plurality of electrical components mounted on the second side ofthe second PCB; at least one electrical conduit between the first PCBand the second PCB, the at least one electrical conduit electricallycoupling the third plurality of electrical components to the edgeconnector and electrically coupling the fourth plurality of electricalcomponents to the edge connector; and a heat spreader comprising athermally conductive material, the heat spreader comprising: a firstportion thermally coupled to the first plurality of electricalcomponents; a second portion thermally coupled to the second pluralityof electrical components and to the third plurality of electricalcomponents; and a third portion thermally coupled to the fourthplurality of electrical components.
 30. The electronic module of claim29, wherein the electronic module is a memory module.
 31. The electronicmodule of claim 29, wherein the first plurality of electricalcomponents, the second plurality of electrical components, the thirdplurality of electrical components, and the fourth plurality ofelectrical components each comprise memory devices.
 32. The electronicmodule of claim 29, further comprising a third PCB having a first sidefacing towards the first PCB and a second side facing away from thefirst PCB, a fifth plurality of electrical components mounted on thefirst side of the third PCB, and a sixth plurality of electricalcomponents mounted on the second side of the third PCB, wherein the heatspreader further comprises a fourth portion, the first portion thermallycoupled to the fifth plurality of electrical components, and the fourthportion is thermally coupled to the sixth plurality of electricalcomponents.
 33. The electronic module of claim 29, further comprising athermally conductive layer between the portions of the heat spreader andthe electrical components.
 34. The electronic module of claim 29,wherein the electrical conduit comprises a flexible electrical conduit.35. The electronic module of claim 29, wherein the electrical conduitcomprises a spacer that supports the second PCB on the first PCB. 36.The electronic module of claim 29, wherein the heat spreader comprises aplurality of separable sections.